1. Field of the Invention
The invention relates to a multi-domain liquid crystal display and its array substrate.
2. Description of the Related Art
Typically, the display contrast ratio and response speed offered by a VA (vertically-aligned) mode liquid crystal display, which uses negative liquid crystal materials and vertical alignment films, are better than a TN (twisted-nematic) mode LCD, since liquid crystal molecules are aligned in a vertical direction when no voltage is applied. Also, it is known the viewing angle performance of a VA mode LCD is improved by setting the orientation directions of the liquid crystal molecules inside each picture element to a plurality of mutually different directions; that is, forming multiple distinct domains in the liquid crystal display.
FIG. 11A shows a schematic diagram illustrating a conventional design of a multi-domain vertically aligned liquid crystal display (MVA LCD). Referring to FIG. 11A, a top substrate 102 and a bottom substrate 104 are both provided with protrusions 106 having different inclined surfaces and covered by vertical alignment films 108. Hence, the liquid crystal molecules 112 near the inclined surfaces orientate vertically to the inclined surfaces to have different degrees of pre-tilt angles. In case the pre-tilt liquid crystal molecules exist, surrounding liquid crystal molecules 112 are tilted in the directions of the pre-tilt liquid crystal molecules 112 when a voltage is applied. Thus, multiple domains each having individual orientation direction of liquid crystal molecules 112 are formed. Besides, the domain-regulating structure for providing inclined surfaces includes, but is not limited to, the protrusions 106, and other structure such as a via structure 114 shown in FIG. 11B may also be used.
However, when one compares the optical path of light I1 and that of light I2 shown both in FIGS. 11A and 11B, it is clearly found the tilted liquid crystal molecules through which the light I2 passes under a field-off state may result in a non-zero phase difference (□nd≠≠0) to cause light leakage. Accordingly, additional compensation films must be provided to eliminate the light leakage.
FIG. 12 shows a schematic diagram illustrating another conventional design of an MVA LCD. Referring to FIG. 12, the transparent electrode 204 on the substrate 202 is provided with slits 206. Because of the fringe fields produced at edges of transparent electrode 204 and at each slit 206, the liquid crystal molecules 208 are tilted toward the center of each slit 206 to result in a multi-domain liquid crystal (LC) cell. However, the strength of the fringe fields generated by the formation of the slits 206 is often insufficient, particularly when the widths and the intervals of the slits 206 are not optimized. Besides, since the azimuth in which the liquid crystal molecules tilt due to fringe fields includes all directions of 360 degrees, a disclination region 210 often appears beyond the slits 206 or between two adjacent slits 206 to result in a reduced light transmittance.
Further, though the protrusion 106, via structure 114, or slit 206 may be provided to create multiple domains, the distribution of these structures in a picture element may reduce the active area for display and thus the aperture ratio of the picture element.